While researching to buy our storm shelter, one of the first questions I asked was if an above-ground storm shelter was as safe as a below-ground shelter. It is logical to think that being underground offers the best protection from wind and debris. Since we have an adult child in a wheelchair who lives with us, a below-ground shelter was not an option.
So, is it safer to be underground when a tornado strikes? Can an above-ground shelter withstand the violent effects of an EF4 or EF5 tornado?
In two articles, I discuss 10 factors to consider when buying a storm shelter and explore the question of which type of home storm shelter is the safest. For many, an underground shelter is impractical or impossible. However, choosing an above-ground shelter is not “settling for second best.” There is no evidence to suggest that an above-ground shelter is less protective than its underground counterpart if built to FEMA guidelines and ICC 500 standards.
An above-ground shelter is typically more accessible to those with mobility challenges and families with small children. This makes it easier and quicker to enter the safety of a storm shelter when seconds matter.
The EF5 tornado that hit Joplin, MO, on May 22, 2011, left a path of destruction over 21 miles long. It tragically killed over 100 and injured more than 1,000. An article written by Adam Jones at the University of Alabama and posted on Phys.org states, “In the damage area, researchers examined 75 residential shelters. Of the 75 shelters observed in Moore, 68 were below ground, and all served their purpose, oftentimes with neighbors of the home with the shelter, the team observed. Only one of the 75 shelters, an above-ground safe room, was penetrated by high-flying debris, a result of errors in building the safe room, the team concluded.”
On May 20, 2013, an EF5 tornado devastated Moore, OK. It killed 24 and injured over 200. An article in The Oklahoman newspaper entitled “Oklahoma tornadoes: Aboveground shelters stood up in face of EF5 Moore tornado” spoke to the effectiveness of above-ground storm shelters. Larry Tanner, a Research Assistant Professor at the National Wind Institute at Texas Tech University, said researchers identified 16 above-ground storm shelters or safe rooms in or near the tornado’s damage path. He confirmed all 16 survived and performed well. He said, “We continue to have great success stories both in Joplin and in Oklahoma City.”
Above-ground safe rooms offer the same near-absolute protection as an underground shelter if they meet FEMA guidelines and the ICC 500 standard. According to FEMA, near-absolute protection means that based on current knowledge of tornadoes and hurricanes, the occupants of a safe room built to FEMA guidance will have a high probability of protection from injury or death.
But…What If?
There will likely always be arguments and questions about the safety of an above-ground storm shelter. What if a tornado drops a train car onto the shelter? What if a tornado throws a large steel I-Beam at the shelter like a missile? This is where the “near-absolute” term may apply. Would a storm shelter survive these scenarios? Maybe, and maybe not. Can any storm shelter keep the occupants safe in 100% of all possible scenarios? Obviously, no.
However, you can extend the “what if” game to below-ground shelters. What if a tornado drops a large truck onto the shelter roof and it collapses? What if the ground-level shelter entrance is blocked and impossible to open? And the shelter fills with water due to a broken water main?
The truth is, no shelter is completely immune from failure. However, below-ground and above-ground shelters have a proven track record of saving lives in EF4 and EF5 tornadoes. According to FEMA (P-361, April 2021), “There has not been a single reported failure of a safe room constructed to FEMA criteria.”
Now, let’s take a closer look the safety of above-ground shelters.
Points Regarding the Safety of an Above-Ground Storm Shelter
Guidelines and Standards
It is critical that an above-ground storm shelter meet or exceed FEMA guidelines and the ICC 500 standard. These publications specify storm shelter design, construction, installation, and testing criteria. FEMA states, “If a safe room meets all of the requirements of FEMA P-361, an above-ground safe room is just as safe as a below-ground or in-ground safe room” (Taking Shelter from the Storm: Building or Installing a Safe Room for Your Home, FEMA P-320, March 2021, 28).
Ensuring Your Shelter Meets FEMA/ICC Requirements
Unfortunately, some companies claim their shelters are “FEMA Certified” or “FEMA Approved” or use similar misleading language. FEMA P-320 and P-361 convey FEMA’s guidance on properly designing and constructing safe rooms. However, FEMA does not actually approve, verify, or certify design calculations or storm shelters. Rather, the licensed design professional who signs the certification attests that the design or product will meet the requirements specified on the certification. FEMA clearly states on its website, “FEMA does not endorse, approve, certify or recommend any contractors, individuals, firms or products. Contractors, individuals, or firms shall not claim they or their products are ‘FEMA approved’ or ‘FEMA certified’”.
So, how do you know if a storm shelter meets the rigorous guidelines and standards? Here are a couple of good ways.
- Look for companies that are members of the American Tornado Shelter Association (ATSA) or the National Storm Shelter Association (NSSA). Both require that member companies design and build storm shelters to the strict FEMA guidelines and ICC 500 standards. The NSSA has an extra membership requirement and consumer benefit. It further requires a third-party review of the design, specifications, and impact test results to ensure compliance. Both associations list member companies on their websites and member companies will display a label on the shelter.
- Companies not belonging to the ATSA or NSSA should provide you with the impact test results and a licensed design professional report attesting that the storm shelter complies with FEMA guidelines and ICC standards. If the company cannot present these reports, I suggest you go elsewhere.
Storm Shelter Requirements
Here are a few topics FEMA guidelines and ICC 500 standards cover. These are high-level bullet points. The guidelines and standards cover these and much more in painstaking detail!
- Construction – Above-ground shelters are typically made of steel, reinforced concrete, or both. While the ICC 500 standard does not mandate specific construction materials, it does set performance criteria that the materials and design must meet to ensure the safety of its occupants.
- Impact Resistance – Residential storm shelters that meet or exceed the FEMA guidelines and the ICC 500 standard are designed to withstand the violent winds and wind-borne debris typical of tornadoes and hurricanes. All storm shelter components, including the door, require missile impact testing to verify they meet the requirements. The standard specifies the testing requirements.
- Anchoring – Above-ground shelters must be anchored to a proper foundation. Proper anchoring prevents the shelter from tipping, moving, or being lifted during a tornado or hurricane.
- Ventilation – The ICC 500 standard defines the requirement for proper ventilation in a shelter. Natural ventilation in a residential storm shelter must be adequate to support the maximum number of occupants the shelter is designed to hold. The standard specifies the venting area required per occupant and the placement of the natural ventilation openings.
- Occupancy and Access – This section sets the minimum usable floor space per occupant and specifies the number of doors and the latching requirements.
The FEMA guidelines and ICC standards cover much, much more. As you can see, storm shelters have extensive engineering, design, installation, and testing specifications. It is critical that any shelter you buy meets FEMA and ICC requirements. Otherwise, you risk buying a shelter that will not stand firm against a violent tornado and everything the storm will throw at it.
All evidence shows that above-ground storm shelters that meet or exceed the FEMA guidelines and ICC 500 standards provide the same level of protection as their below-ground counterpart. If you choose to get an above-ground storm shelter, do so with confidence.
What are your thoughts on the overall safety of an above-ground storm shelter? Let’s discuss this below, or contact me directly.